闽江下游水体硅的组成及营养盐化学计量比

Silicon composition and stoichiometric ratios with other nutrients in the lower Minjiang River,Southeast China

在过去几十年里,河流在人类活动的影响下向沿海生态系统输送不平衡的营养盐负荷导致了严重的区域或全球富营养化问题。闽江受人类活动影响比较明显,为了研究闽江水体营养盐输送比例的变化特征,于2019年7月至2020年7月对闽江下游表层水体碳、氮、磷、硅营养盐进行了季节观测。结果表明:闽江下游表层水体溶解态硅(DSi)、成岩硅(LSi)和生物硅(BSi)的年平均含量分别为5.30、4.58和2.37 mg·L^(-1),但季节性差异大,夏季表现为溶解态硅>成岩硅>生物硅,秋季为溶解态硅>生物硅>成岩硅,而冬季为成岩硅>溶解态硅>生物硅。其中溶解态硅在总硅中的比例沿向海方向呈逐渐降低趋势,而生物硅与之相反。从化学计量比来看,闽江水体明显地受碳、磷限制,基本不受硅、氮限制。据估算,闽江每年向河口输送1.03×10^(10)mol溶解态硅和0.46×10^(10)mol生物硅,并且呈现逐年下降趋势,而碳、氮、磷负荷则呈上升趋势,这种营养盐比例关系会导致河口及近海生态系统结构和功能发生变化。研究闽江水体碳、氮、磷、硅营养盐的化学计量比可为闽江河口及邻近海域水体营养盐结构平衡和富营养化等问题的解决提供理论依据。

Over the past decades,rivers have delivered imbalanced nutrient loads to coastal marine ecosystems due to human activities,which leads to serious regional or global eutrophication problems.The Minjiang River is heavily influenced by human activities.To understand the changing characteristics of nutrient transport ratios in the Minjiang River waters,we measured the seasonal variations of carbon,nitrogen,phosphorus and silicon nutrients in the lower surface waters of the Minjiang River between July 2019 and July 2020.The results showed that the annual average contents of dissolved silicon(DSi),lithogenic silicon(LSi)and biogenic silicon(BSi)in the surface waters of the lower Minjiang River were 5.30,4.58 and 2.37 mg·L^(-1),respectively.There were large seasonal differences among these parameters,with higher content of DSi than LSi and BSi in summer,higher content of DSi than BSi and LSi in autumn and higher content of LSi than DSi and BSi in winter.The proportions of DSi in total silicon tended to decrease gradually from land to sea,while the proportion of BSi was on the contrary.In term of stoichiometric ratios,the Minjiang River mostly presented carbon or phosphorus limitation and was unlimited by silicon or nitrogen.About 1.03×10^(10)mol DSi and 0.46×10^(10)mol BSi were delivered via the Minjiang River to the ocean yearly,showing a decreasing trend year by year.Based on the data in recent years,the nutrient loads of carbon,nitrogen,and phosphorus transported by Minjiang River showed an increasing trend.The imbalanced nutrient loads may lead to changes in the structure and function of the river,estuary,and offshore ecosystems.The study of nutrient stoichiometric ratios can provide a theoretical basis for solving the problems in structural balance of nutrients and eutrophication in Minjiang River estuary and adjacent marine waters.